1. Field of the Invention
The present invention relates to a refrigerant cycle apparatus constituted by connecting a compressor, a gas cooler, a pressure reducing device, an evaporator and the like in an annular shape, using carbon dioxide as a refrigerant, and capable of having a supercritical pressure on a high-pressure side.
2. Description of the Related Art
In this type of refrigerant cycle apparatus, a rotary compressor, a gas cooler, a pressure reducing device (expansion valve, capillary tube, etc.), an evaporator and the like have heretofore been successively piped/connected in an annular shape to constitute a refrigerant cycle (refrigerant circuit). Moreover, a refrigerant gas is sucked on the side of a low-pressure chamber of a cylinder from a suction port of a rotary compression element of a rotary compression, compressed by operations of a roller and a vane to constitute a high-temperature/pressure refrigerant gas, and discharged to the gas cooler from a high-pressure chamber side via a discharge port and a discharge-noise silencing chamber. After the refrigerant gas radiates heat in this gas cooler, the gas is throttled by throttle means, and supplied to the evaporator. There, the refrigerant evaporates, and absorbs heat from surroundings at this time to thereby exert a cooling function.
Here, in recent years, to handle global environmental problems, apparatuses have been developed in which carbon dioxide (CO2) that is a natural refrigerant is used without using conventional chlorofluorocarbon even in this type of refrigerant cycle and in which a transition critical refrigerant cycle is used for operation at a supercritical pressure on a high-pressure side.
In this transition critical refrigerant cycle apparatus, to prevent a liquid refrigerant from being returned into the compressor and compressed, an accumulator has been disposed on a low-pressure side between an outlet side of the evaporator and a suction side of the compressor in such a manner as to accumulate the liquid refrigerant in this accumulator, and suck a gas only into the compressor. Moreover, the pressure reducing device has been adjusted in such a manner that the liquid refrigerant in the accumulator does not return to the compressor (see, e.g., Japanese Patent Publication No. 7-18602).
However, when the accumulator is disposed on the low-pressure side of the refrigerant cycle, more refrigerant charge amount is required. To prevent liquid backflow, a capacity of the accumulator has to be increased, and throttle of the pressure reducing device has to be adjusted. This has resulted in enlargement of an installation space or drop of refrigeration capability in an evaporator 15.
Moreover, since a compression ratio is very high in a case where carbon dioxide is used as the refrigerant of the refrigerant cycle apparatus, it has been difficult to derive a refrigeration capability at high temperature of outside air or the like.